The present invention relates to display devices. The invention is also directed to a technique applicable to display devices each including a driver IC mounted thereon by means of COG bonding.
In liquid-crystal display devices, a plurality of terminals connected to electrodes for applying a driving voltage to liquid crystals, and a plurality of terminals that accept signal lines extending from an external region of a liquid-crystal display panel are formed on a TFT substrate (glass substrate). A driver IC (semiconductor integrated circuit chip) that supplies a driving signal to the electrodes is connected to the former terminals by means of chip-on-glass (COG) bonding. During the COG bonding, an anisotropic conductive film (ACF) that functions as an adhesive, a thermosetting resin or the like laden with electrically conductive particles, is used to electrically interconnect the driver IC and the terminals on the TFT substrate. Bumps are disposed as connection terminals on a side of the driver IC that faces the TFT substrate.
Chip-on-glass (COG) bonding is performed in the following manner: The ACF is overlaid over the plurality of terminal regions of the TFT substrate on which the driver IC is to be mounted, and then after the bumps on the driver IC have been fitted to the terminals on the TFT substrate, a compression bonding head presses the driver IC toward the TFT substrate while heating the IC. This compression of the driver IC under heat spreads the ACF along an upper surface of the TFT substrate. While electrical conduction between the bumps and the terminals on the TFT substrate is being established by the electroconductive particles included in the ACF, the driver IC is mechanically connected to the TFT substrate with the use of the resin in the ACF.
The driver IC is preferably compressed by the compression bonding head when the driver IC is parallel at its lower surface with respect to the upper surface of the TFT substrate. However, if the lower surface of the driver IC is not parallel to the upper surface of the TFT substrate during the compression, there could be partial improper electrical connection between the bumps and the terminals on the TFT substrate.
JP-2008-251828-A (hereinafter referred to as Patent Document 1) discloses measuring resistance between signal input monitoring terminals and signal output monitoring terminals before compressively bonding a driver IC to ensure that an equal force is applied to the driver IC. More specifically, a substrate on which the driver IC is to be mounted includes a signal input monitoring terminal, a signal output monitoring terminal, and a wiring pattern lying between the signal input monitoring terminal and the signal output monitoring terminal. On the substrate the monitoring terminals and the wiring pattern are arranged in four sets in places corresponding to four corners of the driver IC. The wiring patterns are each formed so that when a first bump for monitoring use electrically connects to the signal input monitoring terminals and a second bump for monitoring use electrically connects to the signal output monitoring terminals, electrical connection is established between the signal input monitoring terminals and the signal output monitoring terminals. Resistance values are measured after a total of eight measuring pins have been applied to the four sets of signal input monitoring terminals and signal output monitoring terminals. The balance between the two kinds of monitoring terminals is adjusted in accordance with the timing at which the four resistance values between the signal input monitoring terminals and the signal output monitoring terminals change.